Remove error if config_dict value does not have default type

[nefrathenrici]

This loosens the type restrictions for the YAML files - we can finally have hyperdiff: false!

If the AtmosConfig constructor is unable to convert an input value to the default type, just warn the user and use the given input value:

┌ Warning: Failed to convert `config_dict["hyperdiff"] = false` to default type String, keeping original value

This PR also follows up on #3203, fixing unused YAML keys and adding an exception for the diagnostics key, since it is not found in the default config file.

Example of undesired behavior:

┌ Warning: The configuration passed to ClimaAtmos contains unused keys: diagnostics
└ @ ClimaAtmos /central/scratch/esm/slurm-buildkite/climaatmos-ci/19847/climaatmos-ci/src/solver/yaml_helper.jl:88